A RECORD OF TRANSITION FROM PASSIVE TO CONVERGENT MARGIN AT THE DEVONIAN-CARBONIFEROUS BOUNDARY OF WESTERN LAURENTIA (NORTH AMERICA)

Enigmatic influx of clastic sediments, unconformities and volcanism marked much of western Laurentia at the Devonian-Carboniferous (DC) boundary suggesting the demise of the Paleozoic passive margin. These events were contemporaneous with the Antler orogeny in southwestern Laurentia (WL). However, beyond the type Antler orogeny in southwestern Laurentia, the DC tectonic setting is still unclear. Westerly sediment provenance has been suggested as evidence of a convergent margin setting in a foreland basin. However, there is a gap in our understanding in central WL (Alberta and Montana) despite the fact that paleogeographic reconstructions place this area at the centre of WL. We provide detrital zircon (DZ) U-Pb geochronological data from strata in Alberta (Canada), Montana and Nevada (USA) that are synchronous with the Antler orogeny to constrain sediment dispersal patterns and test the westerly sediment-sourcing hypothesis. We show three DZ- facies specific to particular geographic locations: DZ-facies 1 in southern Nevada (mode at 1430 Ma); DZ facies-2 in northeastern Nevada (mode at 1823 Ma); and DZ-facies 3 in Alberta and Montana (mode at 1036 Ma with depositional age ca. 360-340 Ma). North-south variation in DZ facies indicates that WL basins were locally sourced by recycling of various tectonic fragments having different signatures with input from mid-Paleozoic arc terrane (s). Westerly sourcing is evidenced by the presence of near-depositional ages and affinities of this study’s DZ facies with strata located to the west. Our results and geological evidence from other studies suggest that the Antler Orogeny triggered a depositional shift and controlled sediments dispersal in WL, signaling the demise of the Paleozoic passive margin.